Producing electricity with permanent magnet generators is well known. Such generators generally operate by rotating a shaft having permanent magnets affixed to its surface in a stator, that is generally comprised of copper windings, to produce an electromagnetic current. The permanent magnet generators in general use generally employ rotors comprise of rare earth magnet shafts rotating at speeds, on the order of 150 rpm to 20,000 rpm, within a generator stator. Due to the high strength of the magnets and high operating speed or the very large magnets required at low speeds, the generators are able to produce very high output power densities (defined as the ratio of power output to generator volume). Significant heating of both the generator stator and the rotor is associated with the power density, and this heat can damage the generator windings and demagnetize the rotor if it is not effectively removed from the generator.
The damage and demagnetization caused by excessive heat can result in electo-echanical failure, power loss, or erratic power fluctuation. In some applications such as generator providing electricity for welding generators excessive heat can result in very short and repetitive peak electrical loads
One method of cooling generators is the use of fluids in a closed system within the generator. The disadvantage of fluid cooling generators is that it does not cool the generator rotor shaft, is fairly complex, requiring a circulating pump and a radiator, and it also has the potential to leak fluid and cause damage to the system.
Conventional generator systems are typically cooled by air or hydrogen, both in the form of a forced convective flow within channels and turning regions. An industry requirement for the stator bars within the generator core is that the central region temperature between conducting bars not exceed a preset limit. Many factors influence the maximum central region temperature experienced in operation, including the stator bar design and insulation, the magnetic flux field, the core design, and the cooling design. Air-cooled systems have also been used in permanent magnet generators with varying degrees of success in that most known air-cooled systems can not adequately cool the rotor.
It is known to connect cooling devices to the stator and in this way reduce the heating of the generator and its components. However, due to the spatial arrangement of the stator and the rotor, it is very difficult to provide cooling devices in certain regions of the generator, such as the rotor, that are not very accessible.
Therefore, a need exists for a method or device that can be used for effectively cooling all of the components of a permanent magnet generator, or for a generator that has such a device integral to the generator itself. Such generators, methods, or devices that do not interfere with the spatial arrangement of the stator and rotor, do not run the risk of leaking fluid in the generator, and can effectively cool the rotor would be a significant advantage over the prior art.